In October 1930, Calder paid a visit to the Dutch painter Piet Mondrian
that would change the course of his career. Looking at the colored
rectangles that covered the wall of Mondrian's studio, Calder remarked that
he would like to see them move. After a few experiments in abstract
painting, he began making constructions of wire and wood,
equipping some with a crank or a small motor that could set them in motion
(see Two Spheres within a Sphere and
Pantograph).
"Just as one can compose colors, or forms," Calder said, "so
one can compose motions."

Although abstract, these three-dimensional compositions evoke in their
form and movement representations of planets and other celestial bodies.
"The underlying sense of form in my work has been the system of the
Universe, or part thereof," Calder wrote. "What I mean is that the idea of
detached bodies floating in space, of different sizes and densities,
perhaps of different colors and temperatures, and surrounded and
interlarded with wisps of gaseous condition, and some at rest, while others
move in peculiar manners, seems to me the ideal source of form."